Semiconductor device having an improved structure for preventing cracks, improved small sized semiconductor and method of manufacturing the same

ABSTRACT

According to a typical invention of the inventions disclosed in the present application, a semiconductor chip with an electronic circuit formed therein is fixed to a die pad for a lead frame having projections formed on the back thereof, with an organic dies bonding agent. Pads on the semiconductor chip, and inner leads are respectively electrically connected to one another by metal thin lines. These portions are sealed with a molding resin. Further, each inner lead extends to the outside of the molding resin and is processed into gull-wing form for substrate mounting. Moreover, the inner lead is processed by soldering so that an external terminal is formed. Thus, since the projections are provided on the back of the die pad, the back of a packing material is brought into point contact with that of the die pad as compared with the conventional face-to-face contact. It is therefore possible to minimize the transfer of organic substances from the packing material. Further, since such transfer that a reduction in adhesive property occurs in the back of the die pad, is greatly reduced, the adhesiveness between the upper surface of the die pad and the molding resin is improved, whereby the resistance of SMD to the reflow is enhanced.

This is a Divisional of U.S. Ser. No. 09/695,403, filed on Oct. 25,2000, which is a Divisional of Ser. No. 09/165,295, now U.S. Pat. No.6,177,725, filed on Oct. 2, 1998, which is a Divisional of Ser. No.08/736,610 U.S. Pat. No. 5,864,174, filed Oct. 24, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor device having a structurecapable of preventing cracks produced due to various stresses.

Further, another invention of the present application relates to asemiconductor device capable of being reduced in size and a method ofmanufacturing the semiconductor device.

2. Description of the Related Art

In order to prevent cracks produced in a semiconductor device,techniques described in, for example, Japanese Patent ApplicationLaid-Open Nos. 2-17162 (laid open on May 1, 1990), 2-205351 (laid openon Aug. 15, 1990), 3-259555 (laid open on Nov. 19, 1991), 1-191453 (laidopen on Aug. 1, 1989), 4-84452 (laid open on Mar. 17, 1992) and 6-209055(laid open on Jul. 26, 1994) have been proposed.

Further, techniques described in, for example, Japanese PatentApplication Laid-Open Nos. 4-162736 (laid open on Jun. 8, 1992) and6-37127 (laid open on Feb. 10, 1994) and Japanese Utility ModelApplication Laid-Open No. 4-46551 (laid open on Apr. 21, 1992) have beenproposed to realize a small-sized semiconductor device.

SUMMARY OF THE INVENTION

With the foregoing in view, it is an object of the invention in thepresent application to provide various structures capable of preventingcracks produced in a semiconductor device.

It is an object of another invention in the present application toprovide a small-sized semiconductor device and a method of manufacturingthe semiconductor device.

According to the invention of the present application, for achieving theabove objects, a lead frame equipped with a semiconductor device isprovided with an improved structure, or an improved connection structureis applied to a connection between a semiconductor element and asubstrate provided within a semiconductor device. As an alternative tothis, a stress relaxing material is provided between a substrateequipped with a semiconductor element and a sealing resin.

Further, according to another invention of the present application,there has been proposed a structure in which metal thin lines extendingfrom metallic balls respectively connected to electrodes of asemiconductor element are exposed from the surface of a sealing materialand the surface of each exposed metal thin line has a widthsubstantially equal to the diameter of each metal thin line.

Here, the typical ones of various inventions of the present applicationhave been shown in brief. However, the various inventions of the presentapplication and specific configurations of these inventions will beunderstood from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects, features ofthe invention and further objects, features and advantages thereof willbe better understood from the following description taken in connectionwith the accompanying drawings in which:

FIG. 1 is a view showing the structure of a die pad for a lead frameshowing a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of a semiconductor device (SMD) usingthe lead frame shown in FIG. 1;

FIG. 3 is a view illustrating the structure of a die pad for a leadframe showing a second embodiment of the present invention;

FIG. 4 is a view depicting the structure of a die pad for a lead frameshowing a third embodiment of the present invention;

FIG. 5 is a cross-sectional view of a semiconductor device (SMD) usingthe lead frame shown in FIG. 4;

FIG. 6 is a view illustrating the structure of a die pad for a leadframe showing a fourth embodiment of the present invention;

FIG. 7 is a view depicting the structure of a die pad for a lead frameshowing a fifth embodiment of the present invention;

FIG. 8 is a cross-sectional view of a semiconductor device (SMD) usingthe lead frame shown in FIG. 7;

FIG. 9 is a cross-sectional view of a conventional semiconductor device(SMD);

FIG. 10 is a view for describing a mechanism of occurrence of a failuredue to reflow;

FIG. 11 is a cross-sectional view of a semiconductor device showing asixth embodiment of the present invention;

FIG. 12 is a cross-sectional view of a semiconductor device showing aseventh embodiment of the present invention;

FIG. 13 is a cross-sectional view of a semiconductor device showing aneighth embodiment of the present invention;

FIG. 14 is a cross-sectional view of a plastic molded type semiconductordevice showing a ninth embodiment of the present invention;

FIG. 15 is a cross-sectional view of a plastic molded type semiconductordevice showing a tenth embodiment of the present invention;

FIG. 16 is a configurational view of a semiconductor device showing aneleventh embodiment of the present invention;

FIG. 17 is a cross-sectional view showing the semiconductor device shownin FIG. 16, which has been implemented on a mounting substrate;

FIG. 18 is a cross-sectional view for describing a process formanufacturing the semiconductor device shown in FIG. 16;

FIG. 19 is a view showing the structure of a semiconductor deviceillustrating a twelfth embodiment of the present invention;

FIG. 20 is a cross-sectional view showing the semiconductor device shownin FIG. 19, which has been implemented on a mounting substrate;

FIG. 21 is a cross-sectional view for describing a process formanufacturing the semiconductor device shown in FIG. 19; and

FIG. 22 is a view for describing a method of forming a metal ballconnected to an electrode of a semiconductor element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a view showing the structure of a die pad for a lead frameshowing a first embodiment of the present invention, wherein FIG. 1(a)is a top plan view showing the die pad for the lead frame and FIG. 1(b)is a side view showing the die pad for the lead frame.

As shown in these drawings, a plurality of concave portions 18 a areformed on the upper surface of the die pad 11 of the lead frame and aplurality of projections 18 b are formed on the back of the die pad 11.

As a method of forming the concave portions and the projections, one isused wherein they can be formed simultaneously upon dipless processingeffected on the die pad 11.

FIG. 2 is a cross-sectional view of a surface-mounting semiconductordevice (SMD) using the lead frame showing the first embodiment of thepresent invention.

A general surface-mounting semiconductor device will now be described toprovide easy understanding of the present invention.

FIG. 9 is a cross-sectional view of such a conventional semiconductordevice (SMD).

Referring to FIG. 9, a semiconductor chip 2 with an electronic circuitformed therein is fixed to a die pad 1 with an organic dies bondingmaterial or agent 3. Pads (not shown) on the semiconductor chip 2, andinner leads 4 are respectively electrically connected to one another bymetallic thin lines 5. These portions are sealed with a molding resin 6.

Further, the inner leads 4 extend to the outside of the molding resin 6and are processed into gull-wing form for substrate mounting.Furthermore, the inner leads 4 are processed by soldering to therebyform external terminals 7.

There may be also cases in which in order to make an improvement in theresistance to reflow to be described later, dimples (not shown) areformed on the back of the die pad 1 and countermeasures (also not shown)for defining through holes and slits in the die pad 1 are taken.

However, the above-described conventional semiconductor device (SMD) hasa problem that variations in the resistance to the reflow occuraccording to assembly lots in the case of a thin package in which thethickness of a molding resin is less than or equal to 1.2 mm inparticular. As a result of tracking of its cause, it was found that avery small quantity of paraffin components contained in a lead framepacking material were transferred to the lead frame.

In order to solve such a problem, the packing material is changed and anapproach such as application of the present device to a metallic case orthe like has been invented. However, either case will increase costs anddoes not find satisfaction.

The dimples, through-holes and slits for improving the resistance to thereflow can provide expectation of effects for a mode A to be describedlater. However, since the die pad is reduced in rigidity in regard to amode B, a technically-satisfactory one cannot be obtained.

The term “resistance to reflow” described herein means the limit thatthe SMD is capable of resisting stresses to which it is subject uponactual substrate mounting. As an evaluating method, the following one isknown. Namely, after the SMD is subjected to moisture absorption underdesired conditions, a predetermined temperature profile is placed on theSMD so as to extend over the entire package by an IR reflow device or aVPS device. Next, external cracks of a molding resin are evaluated fromthe outward appearance, internal cracks are evaluated by a sectionhierarchical method or a SAT (Supersonic Crack Test), and the propertyof adhesion between respective interfaces is evaluated by the SAT or azyglo method to thereby determine the resistance to the reflow.

FIG. 10 is a view showing a mechanism in which a failure occurs due tothe reflow.

When a plastic package shown in FIG. 10(a) is used, it takes up moisturefrom the atmosphere during its storage as shown in FIG. 10(b). Theabsorbed moisture is expanded by heat generated upon substrate mountingand thereby failures such as peeling of each interface, cracks, etc.occur.

As described in the mode A, cracks [see FIG. 10(d-1)] have heretoforebeen produced principally due to the peeling and moisture expansion [seeFIG. 10(c-1)] with the back of the die pad defined as the startingpoint. However, a so-called mode B occurs in which owing to theapplication of dimple, through-hole and slit approaches to the die padand an improvement in molding resin, a dies bonding agent takes upmoisture to thereby produce cracks [see FIG. 10(d-2)] due to theseparation of adhesive layers or breakdown/moisture expansion thereof[see FIG. 10(c-2)].

On the other hand, the present invention can realize a lead framecapable of solving the above-described problems and preventing theoccurrence of the cracks due to the peeling of the adhesive layer orbreakdown/moisture expansion thereof due to the moisture absorption ofthe dies bonding agent, and a semiconductor device using the lead frame.

Namely, as shown in FIG. 2, a semiconductor chip 12 with an electroniccircuit formed therein is fixed to a die pad 11 for a lead frame havingprojections 18 b formed on the back thereof, with an organic diesbonding agent 13. Pads (not shown) on the semiconductor chip 12, andinner leads 14 are respectively electrically connected to one another bymetal thin lines 15. These portions are sealed with a molding resin 16.Further, each inner lead 14 extends to the outside of the molding resin16 and is processed into gull-wing form for substrate mounting.Moreover, the inner lead 14 is processed by soldering so that anexternal terminal 17 is formed.

Thus, since the projections 18 b are provided on the back of the die pad11, the back of a packing material is brought into point contact withthat of the die pad as compared with the conventional face-to-facecontact. It is therefore possible to minimize the transfer of organicsubstances from the packing material.

Further, since such transfer that a reduction in adhesive propertyoccurs in the back of the die pad 11, is greatly reduced, theadhesiveness between the upper surface of the die pad 11 and the moldingresin is improved, whereby the resistance of the SMD to the reflow isenhanced.

FIG. 3 is a view illustrating the structure of a die pad for a leadframe showing a second embodiment of the present invention, wherein FIG.3(a) is a top plan view of the die pad for the lead frame and FIG. 3(b)is a side view of the die pad for the lead frame.

As shown in these drawings, a plurality of concave portions 28 a areformed on the upper surface of the die pad 21 of the lead frame and aplurality of projections 28 b are formed on the back of the die pad 21.The concave portions 28 a are formed so as to avoid a semiconductor chipmounting area 29.

Using the lead frame, the SMD is formed in accordance with the sameprocess as the first embodiment.

Since the concave portions 18 a are formed even within the semiconductorchip mounting area in the first embodiment, the dies bonding agent wasrequired in quantity as compared with the conventional one.

However, since the concave portions 28 a are formed so as to avoid thesemiconductor chip mounting area 29 in the second embodiment, thequantity of the dies bonding agent can be saved.

Therefore, the amount of moisture absorbed into a layer of the diesbonding agent does not increase and the cost of the SMD will not be higheither. Even if this structure is adopted, the transfer of organicsubstances from the packing material can be controlled to a minimum.

Accordingly, the property of bonding of the back of the die pad 21 to amolding resin is improved. Further, since water vapor pressure developedupon reflow becomes identical to that in the conventional example, theSMD can make a further improvement in the resistance to the reflow.

FIG. 4 is a view showing the structure of a die pad for a lead frameshowing a third embodiment of the present invention, wherein FIG. 4(a)is a top plan view of the die pad for the lead frame and FIG. 4(b) is aside view of the die pad for the lead frame.

As shown in these drawings, a plurality of grooves 38 a are defined inthe die pad 31 so that a convex ridge 38 b is formed on the back of thedie pad 31 for the lead frame. As a method of forming these, one isknown wherein they can be formed simultaneously upon dipless processingon the die pad 31.

FIG. 5 is a cross-sectional view of a semiconductor device (SMD) usingthe lead frame showing the third embodiment of the present invention.

As shown in the same drawing, a semiconductor chip 32 with an electroniccircuit formed therein is fixed to the die pad 31 of the lead frame,which has the convex ridge 38 b formed on the back thereof with anorganic dies bonding agent 33. Pads (not shown) on the semiconductorchip 32, and inner leads 34 are respectively electrically connected toone another by metal thin lines 35. These portions are sealed with amolding resin 36. Further, each inner lead 14 extends to the outside ofthe molding resin 36 and is processed into gull-wing form for substratemounting. Moreover, the inner lead 14 is processed by soldering so thatan external terminal 37 is formed.

Owing to the above-described construction, the back of a packingmaterial is brought into line contact with that of the die pad 31 ascompared with the conventional face-to-face contact because the convexridge 38 b is formed on the back of the die pad 31. It is thereforepossible to minimize the transfer of organic substances from the packingmaterial. Further, since the convex ridge 38 b is formed on the back ofthe die pad 31, the rigidity of the die pad 31 is improved and a forceresistant to a stress developed upon reflow becomes strong. It istherefore possible to prevent cracks from occurring (reflow failure modeB).

Accordingly, the property of bonding of the back of the die pad 31 tothe molding resin is improved and the resistance of the SMD to thereflow is enhanced because of the high rigidity of the die pad 31.

FIG. 6 is a view illustrating the structure of a die pad for a leadframe showing a fourth embodiment of the present invention, wherein FIG.6(a) is a top plan view of the die pad for the lead frame and FIG. 6(b)is a side view of the die pad for the lead frame.

As shown in these drawings, a plurality of grooves 48 a are defined inthe die pad 41 for the lead frame so that a convex ridge 48 b is formedon the back of the die pad 41. As a method of forming these, one isknown wherein they can be formed simultaneously upon dipless processingon the die pad 41.

In this case, the so-defined grooves 48 a are provided so as to avoid asemiconductor chip mounting area 49.

Using the lead frame, an SMD is formed in accordance with the sameprocess as the third embodiment.

Thus, since the grooves 48 a are provided so as to avoid thesemiconductor chip mounting area 49 in such a manner that the convex 48b is formed on the back of the die pad 41, a dies bonding agent becomesidentical in quantity to the conventional one.

Therefore, the amount of moisture absorbed into a layer of the diesbonding agent does not increase and the cost of the SMD will not be higheither. Even if this structure is adopted, the transfer of organicsubstances from a packing material can be controlled to a minimum andthe rigidity of the die pad 41 can be also increased.

Accordingly, the property of bonding of the back of the die pad 41 to amolding resin is improved and the die pad 41 increases in rigidity.Further, since water vapor pressure developed upon reflow also becomesidentical to that in the conventional example, the resistance of the SMDto the reflow can be further improved.

FIG. 7 is a view illustrating the structure of a die pad for a leadframe showing a fifth embodiment of the present invention, wherein FIG.7(a) is a top plan view of the die pad for the lead frame and FIG. 7(b)is a side view of the die pad for the lead frame.

As shown in these drawings, a wave-shaped portion is formed over theentire surface of the die pad 51 for the lead frame. Namely, a wave top51 a and a wave bottom 51 b are formed. As a method of forming these,one is known wherein they can be formed simultaneously upon diplessprocessing on the die pad 51.

FIG. 8 is a cross-sectional view of a semiconductor device (SMD) usingthe lead frame showing the fifth embodiment of the present invention.

As shown in the same drawing, a semiconductor chip 52 with an electroniccircuit formed therein is fixed to the die pad 51 for the lead frame,which has the wave bottom 51 b formed on the back thereof, with anorganic dies bonding agent 53. Pads (not shown) on the semiconductorchip 52, and inner leads 54 are respectively electrically connected toone another by metal thin lines 55. These portions are sealed with amolding resin 56. Further, each inner lead 54 extends to the outside ofthe molding resin 56 and is processed into gull-wing form for substratemounting. Moreover, the inner lead 54 is processed by soldering so thatan external terminal 57 is formed.

Owing to the above-described construction, the back of a packingmaterial is brought into line contact with that of the die pad 51 ascompared with the conventional face-to-face contact because the wavebottom 51 b is formed on the back of the die pad 51. It is thereforepossible to minimize the transfer of organic substances from the packingmaterial.

In the present embodiment, the wave-shaped portion is formed over theentire surface of the die pad 51. However, the wave-shaped portion maybe partially formed. When the wave-shaped portion is formed so as toavoid a semiconductor chip mounting area, for example, the presentembodiment can bring about the same effect as that obtained in the thirdor sixth embodiment.

Further, the present invention has the following use forms.

(1) The first and second embodiments show the case in which theprojections are provided as the semi-spherical forms. However, they maybe polygonal poles. The shape of each projection is not specified.Similarly, the number of the projections is not specified either.

(2) The third and fourth embodiments show the case in which thecross-section of each groove is semi-spherical. However, the groove maybe V-shaped or U-shaped. The shape of the groove is not specified. Theindividual grooves may be provided separately or continuously. Further,the grooves may run across the die pad or wave-shaped configurations maybe used without sticking to the grooves. Similarly, the number of thegrooves is not specified either.

(3) The first through fourth embodiments have described the method offorming the projections and the grooves simultaneously with the diplessforming process on the die pad. However, they may be formed inaccordance with another process. If a press-processed frame is used,then they may be formed in accordance with a process applied upon theformation of inner leads and a die pad prior to being subjected to aplating process. The method of forming them is not specified oridentified.

According to the above-described construction, the followingadvantageous effects can be brought about:

(1) Since projections are provided on the back of a die pad, thetransfer of organic substances from a packing material can becontrolled.

Further, the property of bonding of the back of the die pad to a moldingresin is improved and the resistance to reflow can be stabilized(variations do not occur depending on assembly lots).

(2) Since the projections are provided on the back of a die pad so as toavoid a semiconductor chip mounting area on the back thereof, the amountof a dies bonding agent can be set identical to the conventional one anda further improvement in the resistance to the reflow can achieved.

(3) Since such transfer that a reduction in adhesive property occurs inthe back of a die pad, is greatly reduced, the adhesiveness between theupper surface of the die pad and a molding resin is improved and theresistance of an SMD to the reflow is enhanced.

(4) Since a convex ridge is formed on the back of a die pad, theproperty of bonding of the back of the die pad to a molding resin can beenhanced by restraining the transfer of organic substances from apacking material. Further, the resistance to reflow can be improved withan increase in rigidity of the die pad.

(5) Since the convex ridge is provided on the back of the die pad so asto avoid a semiconductor chip mounting area, the amount of a diesbonding agent can be saved and the resistance to the reflow can befurther enhanced.

(6) Since the convex ridge is provided on the back of the die pad, theback of the packing material is brought into line contact with that ofthe die pad as compared with the conventional face-to-face contact.Therefore, the transfer of organic substances from the packing materialcan be controlled to a minimum. Further, the rigidity of the die pad canbe improved because the convex ridge is formed. Furthermore, since aforce resistant to a stress developed upon reflow becomes strong, crackscan be prevented from occurring.

(7) Since a wave-shaped portion is formed on a die pad, the property ofbonding of a molding resin to the back of the die pad can be enhanced bycontrolling the transfer of organic substances from a packing material,and the resistance to reflow can be enhanced owing to an improvement inthe rigidity of the die pad.

Sixth through eighth embodiments will next be described below.

FIG. 11 is a cross-sectional view of a semiconductor device showing thesixth embodiment of the present invention.

As shown in the drawing, necessary patterns are formed in advance on asemiconductor element 1 through a thermosetting or thermoplasticadhesive layer 2. Further, a substrate 3 composed of plastic such as aglass epoxy or the like, or ceramic which is reduced by about 0.5 mm to2.0 mm in thickness as compared with the semiconductor element 1 withsoldering balls 4 formed on one surface thereof, is fixed to thesemiconductor element 1 with the adhesive layer 2 interposedtherebetween. A conveying or sealing frame 5 is provided around thesemiconductor element 1. Electrodes 6 on the semiconductor element 1 andconductors 7 on the substrate 3 are respectively connected to oneanother by metal wires 8. Further, they are sealed with a resin 9 sothat the metal wires 8 be covered therewith

Since the present embodiment is constructed in this way, a signal isinput to and output from the semiconductor element 1 through thesoldering balls 4, the substrate 3 and the metal wires 8 when thesemiconductor device is connected to a mother board by soldering withreflow (IR, VPS, air or the like) and is activated. At this time, thesemiconductor element 1 generates heat to thereby produce a thermaldistortion. Alternatively, the semiconductor element 1 produces thermaland mechanical distortions due to external environments. However, sincethe substrate 3 and the adhesive layer 2 serve as cushioning materialsand the electrical connection between the substrate 3 and thesemiconductor element 1 is provided by the metal wires 8, a stressapplied to a connecting portion between the semiconductor element 1 andeach metal wire 8 can be minimized.

Further, the present device can be rendered resistant to variations insource voltage and the like by constructing the substrate 3 in amultilayer form.

The seventh embodiment of the present invention will next be described.

FIG. 12 is a cross-sectional view of a semiconductor device showing theseventh embodiment of the present invention.

As shown in the same drawing, a substrate 3 is bonded onto asemiconductor element 1 with an adhesive layer 2 interposedtherebetween. A sealing frame 5 is provided and electrodes 6 on thesemiconductor element 1 and conductors 7 on the substrate 3 arerespectively electrically connected to one another by metal wires 8. Astructure provided till now is identical to that employed in the firstembodiment.

Thereafter, a plastic or metallic cap 10, which has been processed intoa predetermined shape in advance, is bonded to the sealing frame 5 andthe substrate 3 through a junction layer.

Since the present embodiment is constructed in this way, thesemiconductor element 1 produces a thermal distortion in a mannersimilar to the first embodiment when power is turned ON after thepresent device has been mounted to a mother board. However, since theinterior of the semiconductor device is shaped in the form of a hollowstructure, no stress is applied to a connecting portion between eachelectrode 6 on the semiconductor element 1 and its corresponding metalwire 8 and a connecting portion between each conductor 7 on thesubstrate 3 and its corresponding metal wire 8, whereby the reliabilityof connection is improved.

The eighth embodiment of the present invention will next be described.

FIG. 13 is a cross-sectional view of a semiconductor device showing theeighth embodiment of the present invention. The same elements ofstructure as those employed in the sixth and seventh embodiments areidentified by the same reference numerals and their description will beomitted.

In the present embodiment, as shown in FIG. 3, a thermal conductiveepoxy resin 11 is charged into the inside of the semiconductor deviceand solder balls are provided on a metallic or plastic cap 10 inaddition to the seventh embodiment.

Since the present embodiment is constructed in this way, a semiconductorelement 1 generates heat and thereby produces a thermal distortion inthe same manner as the first and second embodiments when power is turnedON after the present device has been installed on a mother board.However, since the interior of the semiconductor device is filled withthe thermal conductive epoxy resin 11 and the solder balls 12 are formedon the cap 10, the generated heat is dissipated into the mother boardfrom the thermal conductive epoxy resin 11 and the cap 10 through thesolder balls 12. As a result, the thermal distortion can be reduced.

Thus, according to the constructions of the sixth through eighthembodiments, the following advantageous effects can be brought about:

(1) Since a substrate is bonded onto a semiconductor element with anadhesive layer interposed therebetween, and electrodes on thesemiconductor element and conductors on the substrate are respectivelyelectrically connected to one another by metal wires, a semiconductordevice can be rendered high resistant to the heat generation of thesemiconductor element and a thermal stress developed due to externalenvironments. For example, 1000 cycles or more can be achieved on atemperature cycling test.

Since special processing is unnecessary for the semiconductor element, astandard element can be used and new designs and improvements or bumpingor the like is necessary. Thus, the semiconductor device can offer highgeneral versatility.

Further, since solder balls are formed on the substrate in advance,thermal stresses developed upon formation of the balls can be removedand an improvement in reliability can be achieved. Moreover, theresistance of the semiconductor device to reflow can be enhanced byusing ceramic or low moisture-absorbent plastic for the substrate.

(2) Since the interior of the semiconductor device is formed as a hollowstructure, the reliability of its internal connections can be greatlyimproved.

(3) Since the interior of the semiconductor device is filled with athermal conductive epoxy resin and solder balls are provided on a cap inaddition to the above-described effect (2), heat-radiation propertiescan be enhanced after the semiconductor device has been mounted to amother board.

It is thus possible to decrease the thermal distortion and improve thereliability of the internal connections. Further, an improvement in thereliability of electrical connection between the semiconductor deviceand the mother board can be expected.

Ninth and tenth embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings.

FIG. 14 is a cross-sectional view of a resin seal or plastic molded typesemiconductor device showing the ninth embodiment of the presentinvention.

A semiconductor chip 12 is first formed on a substrate 11 by diesbonding. The semiconductor chip 12 is then wire-bonded to the substrate11 by Au wires 13. Thereafter, a substance having a high stress relaxingeffect, such as silicone or the like is applied onto the substrate 11lying around the semiconductor chip 12 as a stress relaxing substance ormaterial so as to form stress relaxing portions 16. These portions areheated and hardened as needed and are sealed with a sealing resin 14.Further, solder balls 15 are provided on the side opposite to thesubstrate 11.

Since the present embodiment is constructed in this way, a stressproduced between the sealing resin 14 and the substrate 11 due to thedifference between their linear expansion coefficients can be relaxed bythe stress relaxing portions 16. As a result, warpage can be reduced.

The tenth embodiment of the present invention will next be described.

FIG. 15 is a cross-sectional view of the resin seal semiconductor deviceshowing the tenth embodiment of the present invention.

In the present embodiment, recesses are defined in a substrate andstress relaxing portions formed by embedding a stress relaxing materialin the recesses are provided.

As shown in the same drawing, recesses 21 a for embedding the stressrelaxing material therein are first defined in a substrate 21 and stressrelaxing portions 27 are provided therein. A substance such as siliconehaving a high stress relaxing effect is used as the stress relaxingmaterial. Next, a semiconductor chip 22 is dies-bonded to the substrate21 having the stress relaxing portions 27 formed by embedding the stressrelaxing material in the recesses 21 a. Further, the semiconductor chip22 is wire-bonded to the substrate 21 by Au wires 23. Thereafter, theseportions are sealed with a sealing resin 24 and solder balls 25 areprovided on the side opposite to the substrate 21.

Since the present embodiment is constructed in this way, a stressdeveloped between the sealing resin 24 and the substrate 21 due to thedifference between their linear expansion coefficients can be relaxed bythe stress relaxing portions 27 formed in the substrate 21. As a result,warpage can be reduced.

According to the above-described construction, the followingadvantageous effects can be brought about:

(1) Since a stress relaxing material is applied between a substrate onthe semiconductor chip side and a sealing resin to thereby form eachstress relaxing portion, the stress produced between the sealing resinand the substrate can be relaxed. As a result, warpage can be reducedand the reliability of connection therebetween can be enhanced.

(2) Since the stress relaxing portions formed by embedding the stressrelaxing material in the surface of the substrate on the semiconductorchip side are provided, the stress produced between the sealing resinand the substrate can be relaxed. Consequently, warpage can be reducedand the reliability of connection therebetween can be improved.

Eleventh and twelfth embodiments of the present invention willhereinafter be described in detail with reference to the accompanyingdrawings.

FIG. 16 is a view illustrating the structure of a semiconductor deviceshowing the eleventh embodiment of the present invention, wherein FIG.11(a) is a cross-sectional view of the semiconductor device and FIG.11(b) is a top plan view of the semiconductor device.

As shown in these drawings, a semiconductor element 11 is sealed with aplastic sealing material 16 so that upper portions of metal thin lines13 respectively electrically connected to electrodes 12 are exposed fromthe surface of the plastic sealing material 16. At this time, the backof the semiconductor element 11 is also exposed from the lower surfaceof the plastic sealing material 16. Incidentally, reference numerals 13a indicate metallic balls.

Here, the plastic sealing material 16 is formed to the required minimumsize to protect the semiconductor element 11.

FIG. 17 is a cross-sectional view of the semiconductor device of theeleventh embodiment of the present invention, which has been mounted toa mounting substrate, in which FIG. 17(a) is a sectional view showingthe entire mounting of the semiconductor device to the mountingsubstrate and FIG. 17(b) is an enlarged sectional view showing themanner in which the semiconductor device has been implemented in themounting substrate.

As shown in these drawings, the semiconductor element 11 is electricallyconnected to substrate electrodes 21 of a mounting substrate 20 throughconductive adhesives 17 while the surface of each metal thin line 13,which has been exposed from the plastic sealing material 16, is beingplaced down. Here, reference numeral 18 indicates the semiconductordevice.

FIG. 18 is a cross-sectional view for describing a process ofmanufacturing the semiconductor device illustrating the eleventhembodiment of the present invention.

(1) As shown in FIG. 18(a), the semiconductor element 11 is electricallyconnected to leads 15 by the metal thin lines 13 in a die pad-freestate. Namely, the semiconductor element 11 is wire-bonded to the leads15.

(2) Next, as shown in FIG. 18(b), the semiconductor element 11 is sealedwith the plastic sealing material 16 so that the back of thesemiconductor element 11 is exposed. At this time, each metal thin line13 is held tight by a mold upon sealing so as to take a shape extendingalong the upper surface of the plastic sealing material 16.

(3) Further, as shown in FIG. 8(c), the upper surface of the plasticsealing material 16 is cut away by a polishing machine 19 so that anexposed width of each metal thin line 13 is sufficiently obtained. Asviewed from a cross section taken along line A—A in FIG. 17(c), a flatwidth d of each metal thin line 13, which has been exposed from theupper surface of the plastic sealing material 16, is formed as shown inFIG. 18(d).

FIG. 19 is a view illustrating the structure of a semiconductor deviceshowing the twelfth embodiment of the present invention, wherein FIG.19(a) is a cross-sectional view of the semiconductor device and FIG.19(b) is a top plan view of the semiconductor device.

As shown in these drawings, a plurality of metallic balls 33 a, 33 b and33 c are respectively joined or connected to electrodes 32 of asemiconductor element 31. Ones of the metallic balls 33 a, 33 b and 33c, which are to be joined to the electrodes 32, are formed to theminimum sizes and the subsequent ones thereof are successively increasedin size.

The semiconductor element 31 is sealed by a plastic sealing material 36so that the upper portion of the top metallic ball 33 c is exposed fromthe surface of the plastic sealing material 36. At this time, the backof the semiconductor element 31 is also exposed simultaneously from thelower surface of the plastic sealing surface 36.

Here, the plastic sealing material 36 is formed to the required minimumsize to protect the semiconductor element 31.

FIG. 20 is a cross-sectional view of the semiconductor device accordingto the twelfth embodiment of the present invention, which has beenmounted to a mounting substrate, wherein FIG. 20(a) is a sectional viewshowing the entire mounting of the semiconductor device to the mountingsubstrate, and FIG. 20(b) is an enlarged sectional view showing themanner in which the semiconductor device has been implemented to themounting substrate.

As shown in these drawings, a semiconductor element 31 is electricallyconnected to substrate electrodes 21 of a mounting substrate 20 throughconductive adhesives 37 while exposed or bare surfaces of metallic balls33 a, 33 b and 33 c are being placed down. Here, reference numeral 38indicates the semiconductor device.

FIG. 21 is a cross-sectional view for describing a process ofmanufacturing the semiconductor device illustrating the twelfthembodiment of the present invention.

(1) As shown in FIG. 21(a), the metallic ball 33 a is first formed onits corresponding electrode 32 of the semiconductor element 31 in a diepad-fee state. Reference numeral 34 a indicates the remainder obtainedby tearing off a metal thin line. A method of forming the metallic ball33 a will now be described as shown in FIG. 22. Namely, as shown in FIG.22(a), the metallic ball 33 a is formed on a metal thin line 34extending from a bonding tool 42 by an electrical charge producedbetween an electrical torch 41 and the metal thin line 34 as shown inFIG. 22(b). Next, as shown in FIG. 22(c), the bonding tool 42 drops sothat the metallic ball 33 a is bonded or joined to its correspondingelectrode 32 of the heated semiconductor element by an ultrasonic waveand its own load. In this condition, a clamp 43 is closed to elevate thebonding tool 42 as shown in FIG. 22(d). In doing so, a force is appliedto the immediately upper portion of the metallic ball 33 a so as to cutthe metallic thin line 34.

(2) Next, as shown in FIG. 21(b), the metallic ball 33 b larger than themetallic ball 33 a in size is formed on the metallic ball 33 a in thesame manner as described above.

(3) Further, as shown in FIG. 21(c), the metallic ball 33 c larger thanthe metallic ball 33 b in size is formed on the metallic ball 33 b.

Incidentally, the above process steps (2) and (3) are repeated severaltimes as needed.

(4) Next, as shown in FIG. 21(d), the semiconductor element 31 is sealedwith the plastic sealing material 36 in such a manner that the reverseside of the semiconductor element 31 is exposed. Since, at this time,each of the metallic balls 33 a through 33 c is held tight by a moldupon sealing, the remainder 34 a of the metal thin line 34, which islocated just above the top metallic ball 33 c, is crushed. As a result,only the top metallic ball 33 c is exposed from the surface of theplastic sealing material 36.

Further, the present invention has the following use forms.

The eleventh embodiment (see FIG. 16) shows an example in which eachelectrode of the semiconductor element is disposed substantially in thecenter of the semiconductor element. However, even if each electrode isdisposed in any portion of the semiconductor element, its position isapplicable to any portion thereof by changing the direction (a wiringangle of a wire loop) of each metal thin line.

The twelfth embodiment (see FIG. 19) shows an example in which theelectrodes of the semiconductor element are disposed around thesemiconductor element (at longitudinally-extending ends thereof.However, the electrodes may be applicable if they are disposed in anyposition of the semiconductor element.

According to the above-described embodiments, the following advantageouseffects can be brought about:

(1) Since there is no by-lead connection, the outside shape of thesemiconductor device can be reduced to the extent of that of thesemiconductor element, whereby the semiconductor device can be reducedin size.

Since the semiconductor element is exposed outside, a high heatdissipation property is obtained.

Further, since each metal thin line is bared over a sufficient length,the area at which each metal thin line is connected to the mountingsubstrate can be greatly ensured. As a result, the reliability ofjunction therebetween can be enhanced.

Furthermore, since the thickness of the plastic sealing material on thesemiconductor element is of the order of the height of a rising portionof each metal thin line, the resultant product can be greatly reduced inthickness as the semiconductor device.

(2) Since the metal thin lines are used as terminals for connections tothe mounting substrate, a process of forming new connecting terminals(bumps or the like) can be omitted. Further, since the already-existingwire bonder can cope with the connecting process, the connectingterminals can be formed by the conventional facility. Thus, themanufacturing cost can be reduced.

Further, since the metal thin lines are held tight by the mold uponplastic sealing, the metal thin lines corresponding to the connectingterminals are disposed on the back of the plastic sealing portion at alltimes. It is therefore possible to easily and reliably materialize theexposure of each metal thin line.

(3) Since there is no by-lead connection, the outside shape of thesemiconductor device can be reduced to the extent of that of thesemiconductor element, whereby the semiconductor device can be reducedin size.

Since the semiconductor element is exposed outside, a high heatdissipation property is obtained.

Further, since the small metallic balls are used with respect to theelectrodes of the semiconductor element, the area of each electrode ofthe semiconductor element can be reduced and the area of a circuitportion of the semiconductor element can be easily ensured. Accordingly,the semiconductor element can be brought into high integration.

Since the large metallic balls are used at the surface exposed portion,the area at which the mounting substrate is joined to each electrode,can be easily ensured.

Accordingly, the area for the connection between the mounting substrateand each electrode can be greatly ensured and the reliability of itsconnection can be enhanced.

Further, since the thickness of the plastic sealing material on thesemiconductor element is of the order of the height of the stackedmetallic balls, the resultant product can be greatly reduced inthickness as the semiconductor device.

(4) Since the metallic balls are used as terminals for connections tothe mounting substrate, a process of forming new connecting terminals(bumps or the like) can be omitted. Further, since the already-existingwire bonder can cope with the connecting process by a simple change insoftware, the manufacturing cost (e.g., costs for introduction of newfacilities) can be reduced.

Further, since the metallic balls are held tight by the mold uponplastic sealing, the metallic balls corresponding to the connectingterminals are disposed on the back of the plastic sealing portion at alltimes and are reliably exposed.

Furthermore, since the metallic balls are held tight by the mold in thesame manner as described above, the remainder obtained by tearing offeach metal thin line lying just above the top metallic ball of themetallic balls is also crushed in the same manner as described above. Asa result, the exposed surface can be formed into a smooth surface freeof bumps and dips.

Since the metallic ball on each electrode of the semiconductor elementis provided in plural form upon holding the metallic ball tight by themold, they serve cushioning functions and the stress exerted on thesemiconductor element can be relaxed. It is therefore possible to avoidproduct defects caused by damage to the semiconductor element.

Moreover, since the polishing processes described in the paragraphs (1)and (2) referred to above can be omitted, the entire process can besimplified so that the assembly cost can be reduced.

While the present invention has been described with reference to theillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to those skilled in the art on reference to this description.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: providing a semiconductor element having a first surface anda second surface, the first surface being opposite to the secondsurface; providing an electrode formed on the first surface of thesemiconductor element; joining a first metallic ball to the electrode ofthe semiconductor element by wire bonding, joining a second metallicball having a diameter larger than that of said first metallic ball ontosaid first metallic ball, and repeating this processing plural times,thereby joining a plurality of metallic balls to said electrode so thatthey are superimposed on said electrode, the metallic balls being formedfrom a metal thin line; and holding a top metallic ball of saidplurality of metallic balls by a mold upon plastic sealing, and exposingthe top metallic ball from the surface of a plastic sealing materialsimultaneously with pressing and flattening of a remainder produced bytearing off the metal thin line; wherein the plastic sealing includescovering the first surface of the semiconductor element, the pluralityof metallic balls up to the top metallic ball, and a portion of the topmetallic ball with the sealing material, the sealing material having asubstantially flat surface; and wherein the exposed surface of the topmetallic ball is disposed in a same plane as the flat surface of thesealing material and is flush with the flat surface of the sealingmaterial, so that the exposed surface is adapted to serve as a terminalfor connecting to a mounting substrate.
 2. A method according to claim1, wherein the second surface of the semiconductor element is exposedfrom the sealing material.
 3. A method according to claim 1, furthercomprising connecting a conductive material with the top metallic ball.